Sunlight contains ultraviolet (UV) radiation, which consists of different types of rays. The types of UV radiation you’re probably most familiar with are UVA and UVB rays. These rays can affect your skin in different ways.

In this article, we’ll take a closer look at the key differences between UVA and UVB rays, how they affect your skin, and what you can do to limit sun damage.

UV radiation is a form of electromagnetic energy. It can come from natural sources, such as sunlight, as well as artificial sources, such as lasers, black lights, and tanning beds.

The sun is the most significant source of UV radiation. It’s the product of a nuclear reaction at the sun’s core, and the radiation travels to earth via the sun’s rays.

UV rays are classified according to wavelength: UVA (longest wavelength), UVB (medium wavelength), and UVC (shortest wavelength).

Here’s a quick comparison of the three main types of UV rays.

Energy levellowestmediumhighest
Skin cells affectedinner cells in the top layer of skin, including dermiscells in the top layer of skinoutermost cells in the top layer of skin
Short-term effectsimmediate tanning, sunburndelayed tanning, sunburn, blisteringredness, ulcers and lesions, severe burns
Long-term effectspremature aging, wrinkles, some skin cancersskin cancer, can contribute to premature agingskin cancer, premature aging
Sourcesunlight, tanning bedssunlight, tanning bedsUVC lights, mercury lamps, welding torches
% of the sun’s UV rays~95~50 (filtered out by the atmosphere)

Here are some important facts about ultraviolet A (UVA) rays and how they affect your skin.

  • They have higher wavelengths, but lower energy levels than other UV rays.
  • They’re more penetrating than UVB rays, which means they can affect cells deeper in the skin.
  • They cause indirect damage to DNA.
  • They cause skin to age prematurely, leading to visible effects such as wrinkles. They’re also associated with some skin cancers.
  • Unlike UVB rays, they’re not absorbed by the ozone layer. About 95 percent of the UV rays that reach the ground are UVA rays.
  • They cause an immediate tanning effect, and sometimes a sunburn. The effects of UVA rays tend to appear right away.
  • UVA rays are the main type of light used in tanning beds.
  • They can penetrate windows and clouds.

Here are some important facts about ultraviolet B (UVB) rays and how they affect your skin.

  • Relative to UVA rays, UVB rays have shorter wavelengths and higher energy levels.
  • UVB rays damage the outermost layers of the skin.
  • They directly damage DNA.
  • UVB rays cause most skin cancers, but they can also contribute to skin aging prematurely.
  • They’re partially absorbed by the ozone layer, but some rays still get through. About 5 percent of the UV rays that reach the ground are UVB rays.
  • Overexposure to UVB rays leads to sunburns. Usually, the effects of UVB rays are delayed, or appear a few hours after sun exposure.
  • Most tanning beds use a combination of UVA and UVB rays. Special UVB-only tanning beds may be touted as safe, but they still cause skin damage. No tanning beds are safe to use or recommended.
  • They don’t penetrate windows, and are more likely to be filtered by clouds.

Ultraviolet C (UVC) rays have the shortest wavelengths and highest energy levels of the three types of UV rays. As a result, they can cause serious damage to all life forms.

Fortunately, UVC radiation is completely filtered out by the ozone layer. As a result, these rays from the sun never reach the ground.

Man-made sources of UVC include welding torches, special bacteria-killing light bulbs, and mercury lamps.

Although not considered a risk for skin cancer, UVC rays can cause severe damage to human eyes and skin, including burns, lesions, and ulcers on the skin.

A number of environmental factors can affect when UV rays are the most powerful. Some of these factors include:

Time of day

UV exposure is highest between 10 a.m. and 4 p.m. During this daily window, the sun’s rays have less distance to cover. This makes them more powerful.


UV exposure is highest in the spring and summer months. During these seasons, the sun is at a higher angle, which increases UV ray intensity. However, the sun can still affect you during fall and winter.


UV exposure is highest in areas on or near the equator, where UV rays have less distance to travel before reaching the ground.


UV rays are more powerful at higher elevations because they have less distance to travel.


The ozone layer provides protection from UV rays. But greenhouse gases and pollutants have caused the ozone layer to thin, increasing UV intensity.


Clouds filter out some UV rays from reaching the ground. However, it depends on the type of cloud. Dark, water-filled clouds may block out more UV rays than high, thin clouds.


UV rays reflect off surfaces such as snow, water, sand, and pavement. This can increase UV exposure.

To keep your skin healthy, it’s important to protect yourself from the sun’s rays, especially if you know you’re going to be outdoors for a length of time.

Consider the following tips to limit sunburn, premature aging, and DNA damage:

Apply sunscreen

Choose sunscreen that offers broad-spectrum protection. This means the sunscreen has the ability to block out both UVA and UVB rays.

A higher sun protection factor (SPF) will provide more protection, but remember that no sunscreen is 100 percent effective at blocking out UV rays. The American Academy of Dermatology (AAD) recommends using a sunscreen that’s 30 SPF or higher.

Sunscreen needs to be reapplied at least every 2 hours or more frequently if you’re sweating, exercising, or swimming. It’s important to know there are no waterproof sunscreens, only those that are water-resistant.

When shopping for sunscreen, you may want to opt for a physical, or mineral-based, product. Recent research has found that the ingredients in some chemical sunscreens can be absorbed into your blood.

At this time, only two sunscreen ingredients — zinc oxide and titanium dioxide — are “generally recognized as safe and effective” (GRASE) by the Food and Drug Administration (FDA). These ingredients are found in physical sunscreens.

Cover up

Clothes can provide some protection from UV exposure. Tightly-woven dry fabrics are best. Many outdoor companies make clothes that provide increased protection from UV rays.

Stay in the shade

Limit your exposure to direct sunlight by staying in the shade. This is most important between 10 a.m. and 4 p.m., when UV rays are stronger.

Wear a hat

A wide-brimmed hat can provide additional protection to your ears and neck.

Wear sunglasses

Choose sunglasses that offer UV protection to prevent damage to your eyes and the surrounding skin.

The sun is one source of vitamin D, which is why it’s sometimes called the “sunshine vitamin.”

However, the AAD advises against getting vitamin D from sun exposure or tanning beds, as UV rays can cause skin cancer.

Rather, they recommend following a healthy diet that includes foods that are natural sources of vitamin D. These include fatty fish like salmon, tuna, sardines, and mackerel.

Vitamin D is also found in maitake mushrooms, egg yolks, and foods and drinks that are fortified with vitamin D, like some milks, breakfast cereals, and orange juice. You may also want to consider taking vitamin D supplements.

Both UVA and UVB rays are capable of damaging your skin.

UVA rays can penetrate your skin more deeply and cause your skin cells to age prematurely. About 95 percent of the UV rays that reach the ground are UVA rays.

The other 5 percent of UV rays are UVB. They have higher energy levels than UVA rays, and typically damage the outermost layers of your skin, causing sunburn. These rays directly damage DNA and are the cause of most skin cancers.